Components of mycobacteria injected in oil/water emulsions into syngeneic tumors growing in the skin of guinea pigs of mice caused the tumors to regress. Animals cured of their tumors were resistant to rechallenge with the same tumor. A mixture of living tumor cells and emulsified, heat-killed BCG cells injected intradermally into guinea pigs with growing dermal tumor and microscopic lymph node metastasis caused eradication of the dermal tumor and lymph node metastases.